The invention concerns a vane pump for conveying bulk substances, in particular meat paste in the form of soupy, boiled or raw sausage base, or pieces of meat or other viscous bulk substances, with
a housing having an inlet and an outlet for the bulk substance, and with
a rotor disposed inside the housing, which displays a rotatably-journaled, central driving element and several moving vanes, which are arranged one behind the other on the driving element in its direction of rotation, and at an angle to the direction of rotation, and that are commonly surrounded by a limiting wall of the housing running in the direction of movement of the vanes, with the limiting wall forming conveying chambers for picking up and transporting the bulk substance, and with rotation of the driving element being moved past the inlet and outlet in sequence.
Known as conveying contrivances for these types of tasks are the screw pump and the vane-cell pump. These types of pumps are generally employed for the continuous or portionwise conveying of meat paste in such manner as to join a hopper-shaped feeding arrangement with a downstream decanting arrangement. From the feeding arrangement the meat paste arrives into the pump via the inlet, which then discharges the meat paste, under pressure, from the outlet into the decanting arrangement. Conveying the meat paste under pressure into the decanting arrangement is a prerequisite for its proper functioning. In order that the bulk substance be capable of being conveyed from the inlet to the outlet, the vanes of the rotor, along with the limiting wall, form conveying chambers that pick up the bulk substance in the region of the inlet and then discharge it again in the region of the outlet. For avoiding air inclusions in the bulk substance and for easier filling, additionally provided is an arrangement for generating a negative pressure or vacuum in the conveying chambers.
A vane pump of the previously-described type is known, for example, from DE-PS (West Germany Patent) 16 53 843. There, disposed in the inner region of the rotor in non-rotatable fashion, but radially displaceable, is a cam on which are supported radially-movable vanes along with their part projecting into the rotor. The cam can be pressed outwardly with the aid of a radial slot guide and a sloping surface. In doing this, it presses in the compression region of the pump on the rear part of the vanes brushing by, which, in this region, are pressed against the limiting wall of the housing such as to bring about an improved sealing action. However, it has been shown that this type of sealing by the vanes is not optimal, because to be precise only one vane at a time can actually lay up tight against the limiting wall of the housing and/or be pressed against this latter. Additionally, an exact radial setting and readjustment of the vanes is not possible, and this known vane pump displays a complicated and expensive construction.
Therefore, proposed in DE-GM (West Germany Utility Model) 89 14 705 is an improved vane pump, where two vanes lying opposed to one another are joined together via a central strut, with a radially adjustable pressure piece being journaled in a radial cutout of the limiting wall, which replaces the contour of the limiting wall with its surface facing toward the vanes. The pressure piece presses the vanes against the oppositely-lying wall, in a region shortly ahead of the pump outlet. In this way, at least two vanes can be constructed pressure tight, and therewith a conveying chamber.
Also known are types of vane pumps where the vanes are axially displaceable, however being otherwise sealed in similar fashion by pressing against the limiting wall, like in the case of the previously described, known vane pumps.
With all customary type vane pumps, sealing is accomplished only by pressing the vanes against the limiting wall of the housing. The consequence is an undesired friction between vanes and housing and, therewith, a not inconsiderable wear of the vane pump, so that frequent maintenance of the vane pump (in particular by replacement of the stator, of the rotor or at least the vanes) is indispensable. Because of the wear, the conveying cell is no longer pressure tight. Hence, efficiency is worsened by backflow losses, and, therewith, the precision of portioning is decreased in disadvantageous fashion.